Optical scanner system having a laser beam power attentuation mechanism

ABSTRACT

An optical scanner assembly for exposing an image on a scanned surface. The optical scanner assembly includes a laser mechanism for producing a laser beam representative of the image to be exposed on the scanned surface. The laser beam defines an optical path between the laser mechanism and the scanned surface. A laser beam shaping system is positioned along the optical path for focusing and shaping the laser beam onto the scanned surface. A scanning and directing system is provided for directing the laser beam to the scanned surface and scanning the laser beam across the scanned surface in an image-wise pattern. A unibody attenuation mechanism is positioned along the optical path for power attenuation of the laser beam, wherein the unibody variable density power attenuation mechanism is a linear density wedge.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical scanner assembliesand laser imaging systems incorporating such scanners. In particular,the present invention relates to an internal drum type optical scannerassembly having a unibody laser beam power attenuation mechanism,including a variable density attenuator, suitable for use in a medicalimaging system.

Laser imaging systems are commonly used to produce photographic imagesfrom digital image data generated by magnetic resonance (MR), computedtomography (CT) or other types of scanners. Systems of this typetypically include a continuous tone laser imager for exposing the imageon photosensitive film, a film processor for developing the film, and animage management subsystem for coordinating the operation of the laserimager and the film processor.

The digital image data is a sequence of digital image valuesrepresentative of the scanned image. Image processing electronics withinthe image management subsystem processes the image data values togenerate a sequence of digital laser drive values (i.e., exposurevalues), which are input to a laser scanner. The laser scanner isresponsive to the digital laser drive values for scanning across thephotosensitive film in a raster pattern for exposing the image on thefilm.

The continuous-tone images used in the medical imaging field have verystringent image-quality requirements. A laser imager printing ontotransparency film exposes an image in a raster format, the line spacingof which must be controlled to better than one micrometer. In addition,the image must be uniformly exposed such that the observer cannot noticeany artifacts. In the case of medical imaging, the observers areprofessional image analysts (e.g., radiologists).

Optical scanning assemblies are used to provide uniform exposure of theimage on photosensitive film. The optical scanning assemblies combine alaser system with unique optical configurations (i.e., lenses andmirrors), for uniform exposure of the image onto the film. Past opticalscanning assemblies used for achieving the level of performance requiredby the medical imaging industry utilize costly components incorporatedinto complex optical scanning systems. Such systems often combinecomplex, multi-sided mirrors and lens configurations for directing thelaser beam onto a moving or stationary photosensitive film.

Known laser imagers used for medical imaging include a polygonal scanneror a galvanometer scanner. For example, a commonly used polygonalscanner configuration has a polygonal mirror repetitively exposingsuccessive raster lines onto a sheet of moving photosensitive film. Theoptics must focus the laser beam over a flat image line and compensatefor facet-to-facet angular errors in the polygon. These functions haveusually been accomplished with combinations of costly precision groundanti-reflection coated glass lenses. The film is moved at a constantspeed on rollers where the film is placed at the focus of the scanninglaser beam. The film must be moved with a surface velocity constant tobetter than about 0.5%. Momentary disturbances or perturbations in themotion of the film, such as those caused by striking a film guide,position sensor or nip roller, can cause serious "glitches" in theexposed image, resulting in poor image quality. Avoidance of suchperturbations requires that the film path during imaging be free of suchobstructions. Such a film path often occupies a considerable amount ofspace in the laser imaging device.

Another known example of an optical scanner used for laser imagingincludes a galvanometer optical scanner assembly having adual-galvanometer configuration. The dual-galvanometer configurationincludes one galvanometer mirror which repetitively sweeps the laserbeam to form the raster lines, while a second, slower-movinggalvanometer mirror deflects the raster lines down the page of thephotographic film. The film, held motionless during exposure, is usuallyheld in a curved platen to avoid the necessity of flattening the imagefield in both directions. While problems due to film motion areeliminated, since the film can be curved in only one direction at once,such a configuration requires the use of field-flattening optics for itsoperation. The use of galvanometers, on the other hand, offers relieffrom the problem of facet-to-facet errors found in polygon-based scannersystems. Galvanometers, like accurate polygon spinners, are precisioninstruments, and therefore, are very expensive to manufacture.

In light of the known drawbacks of present laser imaging devices, it isdesirable to have an optical scanner which does not rely on expensivemirror and optical configurations to compensate for errors inherent inthe scanner design. It is desirable to have an optical scanner for usein a laser imager which does not require an extraordinary amount ofspace nor which requires space considerations due to the introduction ofglitches from the film path. Further, it is desirable to have an opticalscanner for use with a laser imager which meets the image-qualityrequirements of the medical imaging industry.

SUMMARY OF THE INVENTION

The present invention is directed to an optical scanner assembly havinga unibody beam power attenuation mechanism, for use in a laser imager.The optical scanner assembly is capable of producing images which meetthe image-quality requirements of the medical imaging industry. Further,the novel configuration of the optical scanner in accordance with thepresent invention does not require the use of a complex or expensivelymanufactured scanner and lens system.

In one exemplary embodiment, the present invention includes an opticalscanner assembly for exposing an image on a scanned surface. The opticalscanner assembly includes a laser mechanism for producing a laser beamrepresentative of the image to be exposed on the scanned surface. Thelaser beam defines an optical path between the laser mechanism and thescanned surface. A laser beam shaping system is positioned along theoptical path for focusing and shaping the laser beam onto the scannedsurface. A scanning and directing system is provided for directing thelaser beam to the scanned surface and scanning the laser beam across thescanned surface in an image-wise pattern. A unibody variable densityattenuator mechanism is positioned along the optical path for powerattenuation of the laser beam, wherein the unibody attenuation mechanismis a linear density wedge.

The laser beam shaping system includes a first cylinder lens positionedalong the optical path for shaping and focusing the laser beam in afirst direction, and a second cylinder lens positioned along the opticalpath for shaping and focusing the laser beam in a second direction. Theunibody attenuator mechanism has an attenuation orientation which isoriented in the same direction as the second cylinder lens. In onepreferred application, the unibody attenuator mechanism is locatedadjacent the second cylinder lens. The second cylinder lens has afocusing spot at the scanned surface, wherein the combination of theunibody attenuator mechanism and the second cylinder lens does notaffect the focusing spot at the scanned surface.

The unibody attenuator mechanism can be adjustable. In one embodiment,the optical scanner assembly further includes an adjustment mechanismcoupled to the unibody attenuator mechanism for adjusting the amount ofpower attenuation of the laser beam. The adjustment mechanism foradjusting the unibody attenuator mechanism may adjust the position ofthe unibody attenuator mechanism in a direction perpendicular to theoptical path. The adjustment mechanism for adjusting the unibodyattenuator mechanism can include a screw motor.

The unibody attenuator mechanism can be a very bold density attenuationmechanism. The unibody attenuation mechanism includes a first end and asecond end, wherein the degree of attenuation varies between the firstend and the second end. In one embodiment, the unibody attenuationmechanism is positioned substantially perpendicular to the optical pathhaving the laser beam passing therethrough, and wherein the attenuationof the laser beam increases as the laser beam is moved from a positionproximate the first end to a position proximate the second end.

The unibody attenuation mechanism includes a first side and a secondside, wherein the unibody attenuation mechanism shifts the position ofthe laser beam as it passes through the unibody attenuation mechanismfrom the first side to the second side.

The unibody attenuation mechanism further includes an attenuator supportsubstrate having a major surface. A varying reflective material coversthe major surface. The support substrate can be constructed of glass.The varying reflective material can be a metallic material. In oneapplication, the attenuation support substrate includes a first end anda second end, wherein the reflectivity density of the varying reflectivematerial increases from the first end to the second end. In anotherapplication, the unibody attenuation mechanism is partiallytransmissive. The attenuator support substrate includes a first end anda second end, wherein the transmissive properties of the varyingreflective material decreases from the first end to the second end.

In another exemplary embodiment, the present invention includes anoptical scanner assembly used in an internal drum type scanner forexposing an image on a photosensitive film. The optical scanner assemblyincludes a laser mechanism for producing a laser beam representative ofthe image to be exposed on the photosensitive film. The laser beamdefines an optical path between the laser mechanism and thephotosensitive film. A laser beam shaping system is positioned along theoptical path for focusing and shaping the laser beam. A scanning anddirecting system is provided for directing the laser beam and scanningthe laser beam radially across the photosensitive film in an image-wisepattern. A unibody attenuator mechanism having a first end and a secondend, wherein the degree of attenuation varies from the first end to thesecond end is provided. The unibody attenuator mechanism is positionedalong the optical path for power attenuation of the laser beam. Theunibody attenuator mechanism may be adjustable.

In yet another exemplary embodiment, the present invention is a laserimaging system. The laser imaging system includes a film feed mechanism,a film exposure mechanism, a film processor mechanism, and a filmreceiving area. A film transport system is provided for moving a pieceof photosensitive film between the film feed mechanism, the filmexposure mechanism, the film processor mechanism, and the film receivingarea. The film exposure mechanism includes an optical scanner assemblyhaving a unibody attenuation mechanism for power attenuation of a laserbeam passing therethrough. The optical scanner assembly is preferably aninternal drum type scanner.

The advantages of the present invention will be set forth in part in thedescription that follows and in part will be apparent from thedescription or may be learned by practice of the invention. Theadvantages of the present invention will be realized and attained bymeans particularly pointed out in the written description and claims, aswell as in the appended drawings. It is to be understood, however, thatboth the foregoing general description and the following detaileddescription are exemplary and explanatory only, and not restrictive ofthe present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the present invention and together with thedescription serve to explain the principles of the invention. Otherobjects of the present invention and many attendant advantages of thepresent invention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, in which likereference numerals designate like parts throughout the figures:

FIG. 1 is an elevational diagram of a laser imaging apparatus inaccordance with the present invention;

FIG. 2 is a perspective view of an exemplary film exposure assemblyhaving an optical scanner assembly for use in a laser imaging apparatus,in accordance with the present invention;

FIG. 3 is an end view of the film exposure assembly shown in FIG. 2;

FIG. 4 is a block diagram illustrating an exemplary optical scannerassembly laser beam shaping and directing system in accordance with thepresent invention;

FIG. 5 is a perspective view of one exemplary embodiment of an opticalscanner assembly laser beam shaping and directing system in accordancewith the present invention;

FIG. 6 is an optical diagram in the cross-scan direction illustrating anexemplary embodiment of the optical scanner laser beam shaping anddirecting system shown in FIG. 5;

FIG. 7 is an optical diagram in the cross-scan direction illustrating anexemplary embodiment of the optical scanner assembly laser beam shapingand directing system shown in FIG. 5;

FIG. 8 is an optical diagram in the in-scan direction illustrating anexemplary embodiment of the optical scanner assembly laser beam shapingand directing system shown in FIG. 5;

FIG. 9 illustrates an exemplary embodiment of an optical configurationsuitable for use in an optical scanner assembly in accordance with thepresent invention;

FIG. 9a is a perspective diagram illustrating the orientation of lens L1and lens L2;

FIG. 10 is a graph illustrating focal length versus tilt angle for oneexemplary embodiment of a lens in FIG. 9;

FIG. 11 is a cross-sectional view of one exemplary embodiment of a lensshown in FIG. 9;

FIG. 12 is a longitudinal cross-sectional view of an exemplaryembodiment of a lens shown in FIG. 9;

FIG. 13 is a perspective view illustrating a step in a manufacturingprocess of forming a lens shown in FIG. 9;

FIG. 14 is a perspective view illustrating another step in amanufacturing process of forming a lens shown in FIG. 9;

FIG. 15 is a perspective view illustrating another step in amanufacturing process of forming a lens shown in FIG. 9;

FIG. 16 is a block diagram illustrating an exemplary embodiment of alaser beam feedback control system for use in an optical scanner system,in accordance with the present invention;

FIG. 17 is a top view of an exemplary embodiment of the use of a lens asa beamsplitter in a laser feedback control system, in accordance withthe present invention is shown;

FIG. 18 is a side view illustrating one exemplary embodiment of the useof a lens as a beamsplitter in a laser feedback control system, inaccordance with the present invention;

FIG. 19 a top perspective view of an exemplary embodiment of a flexiblecylinder lens in accordance with the present invention;

FIG. 20 illustrates an edge view of the flexible cylinder lens shown inFIG. 19 in a curved position;

FIG. 21 illustrates another exemplary embodiment of an edge view of theflexible cylinder lens shown in FIG. 19 in a flexed or curved position;

FIG. 22 is a cross-sectional view of one exemplary embodiment of theflexible cylinder lens illustrated in FIG. 19;

FIG. 23 illustrates a longitudinal cross-sectional view of an exemplaryembodiment of the flexible cylinder lens shown in FIG. 19;

FIG. 24 is a perspective view illustrating an exemplary embodiment of astep in a manufacturing process of forming the lens shown in FIG. 19;

FIG. 25 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 26 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 27 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 28 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 29 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 30 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 31 is a perspective view illustrating an exemplary embodiment ofanother step in a manufacturing process of forming the lens shown inFIG. 19;

FIG. 32 illustrates a perspective view of an exemplary embodiment of anattenuator for use with an optical scanner assembly, in accordance withthe present invention;

FIG. 33 is a top view of the attenuator shown in FIG. 32;

FIG. 34 illustrates a longitudinal cross-sectional view of oneembodiment of the attenuator in accordance with the present invention,taken along line 34--34 of FIG. 33;

FIG. 35 is a graph of optical density versus distance for one exemplaryembodiment of the attenuator shown in FIG. 33;

FIG. 36 is an optical diagram illustrating an exemplary embodiment ofthe effect of a laser beam passing through the attenuator in accordancewith the present invention;

FIG. 37 is a graph illustrating an exemplary embodiment of the intensityof the laser beam relative to a center axis before it passes through theattenuator shown in FIG. 36;

FIG. 38 is a graph illustrating an exemplary embodiment of the intensityof the laser beam relative to a center axis after it passes through theattenuator shown in FIG. 36;

FIG. 39 is a block diagram illustrating one exemplary embodiment of amotor control system for calibration of an attenuator in accordance withthe present invention;

FIG. 40 is a first perspective view illustrating an exemplary embodimentof an optical scanner assembly for use in a laser imager in accordancewith the present invention;

FIG. 41 is a rear perspective view illustrating the optical scannerassembly shown in FIG. 40; and

FIG. 42 is a block diagram illustrating one exemplary embodiment ofoperation of an optical scanner assembly in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an elevational diagram illustrating an exemplary embodiment ofa laser imaging system 30 suitable for use in the medical imagingindustry including an optical scanner assembly, in accordance with thepresent invention. The imaging system 30 includes a film supplymechanism 32, a film exposure assembly 34, a film processing station 36,a film receiving area 38, and a film transport system 40. The filmsupply mechanism 32, film exposure assembly 34, film processing station36, and film transport system 40 are all located within an imagingsystem housing 42.

Photosensitive film is stored within the film supply mechanism 32. Thefilm transport system 40 allows the photosensitive film to be movedbetween the film exposure assembly 34, film processing station 36, andthe film receiving area 38. The film transport system 40 may include aroller system (not shown) to aid in transporting the film along a filmtransport path, indicated by dashed line 44. The direction of filmtransport along film transport path 44 is indicated by arrows 46. Inparticular, the film supply mechanism 32 includes a mechanism (notshown) for feeding a piece of film along film transport path 44 into thefilm exposure assembly 34 for exposing the desired image on thephotosensitive film using the optical scanner assembly in accordancewith the present invention. After exposure of the desired image on thephotosensitive film, the photosensitive film is moved along the filmtransport path 44 to the film processing station 36. The film processingstation 36 develops the image on the photosensitive film. After filmdevelopment, the photosensitive film is transported to the filmreceiving area 38.

In FIG. 2, a top perspective view of one exemplary embodiment of thefilm exposure assembly 34 including an optical scanner assembly inaccordance with the present invention is shown. The film exposureassembly 34 has an internal-drum type configuration. In the exemplaryembodiment shown, the film exposure assembly 34 includes an opticalscanner assembly 50 (better seen in FIG. 3) mechanically coupled to anoptics translation system 52, mounted within drum 54 for exposure of thefilm. The center of curvature of the drum 54, which is located along thedrum longitudinal axis, is indicated by dashed line 56. During ascanning process, the optics translation system 52 operates to move theoptical scanner assembly 50 along the longitudinal axis 56, indicated bydirectional arrow 58, and after scanning, returns the optical scannerassembly 50 to a start position, along the longitudinal axis 56,indicated by directional arrow 60.

Referring also to FIG. 3, an end elevational view of the film exposureassembly 34 is shown. Drum 54 includes a film platen 62 having aninternal drum surface 64. During exposure of a photosensitive film 66,the photosensitive film 66 is held against the internal drum surface 64,which has a cylindrical or partial cylindrical shape.

In general, the photosensitive film 66 is held against the film plateninternal drum surface. The optical scanner assembly 50 scanning laserbeam (indicated at 68) emanates radially from the center of curvature ofthe drum 54, which is located along the drum longitudinal axis 56. Theoptical scanner assembly 50 scans the laser beam containing image datarepresentative of the image to be exposed in raster lines by rotatingabout the longitudinal axis 56 of the cylinder drum. As the opticalscanner assembly 56 scans the image in raster lines on photosensitivefilm 66 located on the internal surface of the drum 64, the opticstranslation system 52 moves the optical scanner assembly 50 along thelongitudinal axis 56 to expose the full image on the photosensitivefilm. The optical scanner assembly in accordance with the presentinvention is described in detail later in this specification.

In one exemplary embodiment, the film exposure area on the internal drumsurface is 17 inches by 14 inches, suitable for exposure of a 17 inch by14 inch piece of photosensitive film. In the exemplary embodimentdisclosed herein, the film is exposed in a vertical direction. Inparticular, since the 14 inch edge of the film is fed into the exposuremodule and subsequently scanned in the 17 inch direction, the scannedraster lines appear in the vertical direction. The laser beam is scanned180° across the internal drum surface, for exposure of 17 inches acrossthe photosensitive film. The optics translation system moves the opticalscanner assembly along the longitudinal axis located at the center ofcurvature of the internal drum surface for a distance of 14 inches, forfull exposure of the desired image/images on photosensitive film.

The photosensitive film can be a photosensitive film which is sensitiveto laser beam light. In one exemplary embodiment, the film is a lightsensitive photothermographic film having a polymer or paper base coatedwith an emulsion of dry silver or other heat sensitive material. Oneknown film suitable for use in medical imaging processes with theoptical scanner assembly in accordance with the present invention iscommercially available under the tradename Dryview Imaging Film (DVB orDVC), manufactured by Imation Corp. of Oakdale, Minn.

The optical scanner assembly, components of the optical scannerassembly, and operation of the optical scanner assembly are described indetail in the following paragraphs.

Optical Scanner Assembly

1. Laser Beam Shaping and Directing System.

The optical scanner assembly in accordance with the present inventionincludes a laser beam shaping and directing system. In FIG. 4, a blockdiagram of one exemplary embodiment of a laser beam shaping anddirecting system in accordance with the present invention is generallyshown at 70. As shown in FIG. 4, the laser beam shaping and directingsystem includes a controller 72, a laser driver 74, a laser assembly 76,first optical mechanism 78, second optical mechanism 80, a scanning anddirecting system 82 positioned in optical alignment with photosensitivefilm 66. Controller 72 provides an image signal 84 to laser driver 74representative of the image to be exposed on the photosensitive film 66.Controller 72 also provides control signals to and receives controlsignals from scanning and directing system 82, indicated at 85. Laserdriver 74 is responsive to image signal 84 for providing an outputdriver signal 86 to laser assembly 76. In response to output driversignal 86, laser assembly 76 emits (produces) a laser beam which isrepresentative of the image to be exposed on the photosensitive film 66.The first optical mechanism 78, second optical mechanism 80 and scanningand directing system 82 function together to shape, focus, and directthe laser beam 88 for exposing the desired image or images on thephotosensitive film 66.

The first optical mechanism and second optical mechanism shape the laserbeam in two separate directions, which are generally perpendicular toeach other. The first optical mechanism 78 includes a lens system whichfunctions to shape the laser beam 88 profile in a first direction (butnot a second direction) for focusing the laser beam 88 in a firstdirection on the film 66. The second optical mechanism 80 includes alens system which functions to shape the laser beam 88 in the seconddirection (but not the first direction) for focusing the laser beam 88in the second direction onto the photosensitive film 66. Scanning anddirecting system 82 includes a scanner and mirror system for directingthe laser beam 88 to the desired location on film 66 and scanning thelaser beam 88 across the film surface in a raster pattern for exposingthe desired image on film 66.

In FIG. 5, a perspective view of one exemplary embodiment of an opticalscanner assembly laser beam shaping and directing system in accordancewith the present invention is generally shown. As shown in FIG. 5, thelaser beam shaping and directing system 70 includes a laser diode 132, alaser collimator 134, a lens L1, a lens L2, a folding mirror M1, ascanner assembly 136, including a scanner motor 138 and a scanner mirrorM2, a flexible lens L3, a feedback sensor 140, an absorbing surface 142,and an absorbing surface 144. As shown in FIG. 5, laser diode 132 andlaser collimator 134 comprise the laser assembly 76. First opticalmechanism 78 includes lens L1 and lens L3. Second optical mechanism 80includes lens L2. The scanning and directing system 82 includes foldingmirror M1 and scanner assembly 136, including scanner motor 138 andscanner mirror M2.

Laser diode 132, laser collimator 134, lens L1, lens L2, folding mirrorM1, scanner mirror M2, and flexible lens L3 are in optical alignment(along a path as defined by laser beam 88) for shaping, focusing anddirecting laser beam 88 between laser diode 132 and a photosensitivefilm. In the particular embodiment shown, lens L1 is opticallypositioned between lens L2 and laser collimator 134. Lens L2 isoptically positioned between lens L1 and folding mirror M1. Foldingmirror M1 is optically positioned between lens L2 and scanner mirror M2.Scanner mirror M2 is optically positioned between folding mirror M1 andlens L3. Lens L3 is optically positioned between scanner mirror M2 andthe film 66. It is recognized that the above laser beam shaping anddirecting system 70 elements may be alternately configured within thescope of the present invention, such as lens L2 being in opticalalignment between collimator 134 and lens L1, and lens L1 being inoptical alignment between lens L2 and folding mirror M1.

In summary, the laser diode 132 is electrically coupled to laser driver104 (shown in FIG. 4). The laser diode 132 emits laser beam 88 throughlaser collimator 134 such that the collimated laser beam 88 is auniformly shaped light source (modulated in an image-wise pattern),representative of the image to be exposed on the film. In one preferredembodiment, the collimated laser beam 88 is generally elliptical shaped.

The laser beam 88 is transmitted through lens L1, transmitted throughlens L2 and is reflected by the folding mirror M1 such that it isincident on the scanner mirror M2. In one preferred embodiment, thescanner mirror M2 is a two-sided mirror which is mounted on the shaftthrough an adapter 137 of scanner motor 138. In one embodiment, thescanner motor 138 is a DC brushless motor.

Upon operation of scanner motor 138, the scanner mirror M2 is rotatedand the laser beam 88 is reflected outward radially in an approximateconical shape and transmitted through flexible lens L3 for exposing thefilm 66 in a raster pattern. Both sides of scanner mirror M2 are usedfor directing the laser beam 88 through flexible lens L3 to expose thefilm 66. In one embodiment, the laser beam 88 and the motor axis form anangle that is nominally 84°.

In one exemplary embodiment, lens L1, lens L2, and flexible lens L3 arecylinder lenses, and in particular, are cylinder lenses having aplano-convex optical configuration. A plano-convex cylinder lens is alens having a straight side (i.e., planar) and a convex or curvedopposite side. Lens L1 has its convex side facing lens L2. Lens L2 hasits convex side facing folding mirror M1, and flexible lens L3 has itsconvex side facing the film 66. Lens L1 and lens L2 are positioned suchthat the focusing directions are perpendicular to each other, and assuch, lens L1 shapes laser beam 88 in the cross-scan direction, and lensL2 shapes laser beam 88 in the in-scan direction. Each of these lensesand the effect of their orientation will be described in detail later inthe specification.

With the present invention, all of the optical elements, including lensL1, lens L2 and flexible lens L3, are tilted from a perpendicularposition relative to the optical axis. As such, all of the reflectedbeams (reflected portions of the laser beam) can be controlled such thatthey are dumped onto absorbing surfaces to eliminate light scatteringfrom reflected beams or otherwise used. By controlling the reflectedbeams, lens L1, lens L2, and flexible lens L3 do not require costlyanti-reflective coatings.

In particular, lens L1 and lens L2 are tilted relative to an opticalpath defined by the laser beam 88. In particular, lens L1 and lens L2each include a longitudinal axis and a transverse axes extendingtherethrough. Lens L1 and lens L2 transverse axis are perpendicular toeach other, and perpendicular to the optical path. The lens L1 and lensL2 longitudinal axes are not perpendicular to the optical path, beingangled or "tilted", and are rotated about their respective transverseaxis. As will be described later in the specification, the tilt in lensL2 may be used to aid in focusing laser beam 88 at a desired location(for the scanned surface). Further, the reflected beam from tilted lensL1 provides a feedback signal 147 to feedback sensor 140. Operation ofthe lens feedback system will also be described later in thespecification. Lens L2 is also tilted to allow a portion of the laserbeam 88 which reflects off the surface of the lens L2, indicated asreflected beam 146, to be dumped onto absorbing surface 142, such thatit does not generate undesirable stray light or spurious film exposures.

Flexible lens L3 is tilted from a perpendicular position relative to theoptical axis as defined by the laser beam. As such, a portion of laserbeam 88 reflects off of flexible lens L3, indicated at 148, and isdumped onto another absorbing surface 144 instead of reflecting directlyback into the optics module. Similarly, the optical axis of the laserbeam 88 passing through flexible lens L3 is not perpendicular to theposition of the film, and as such, the reflected beam 147 from the filmis also dumped to an absorbing surface 149 to avoid light scattering. Inone embodiment, the incident angle of the laser beam 88 relative to anaxis perpendicular to the flexible lens L3 and the film is nominally 6°.

In FIG. 6, an optical diagram illustrating beam shaping in thecross-scan direction is shown. In the exemplary embodiment shown, lensL1 and flexible lens L3 cooperate to focus the laser beam 88 on the film66 in the cross-scan direction. In particular, laser assembly 76 emitscollimated laser beam 88 which is representative of the image to beformed on photosensitive film 66, indicated at 152. As laser beam 88passes through lens L1 (153), lens L1 acts to focus the laser beam 88 atthe position of the spinning mirror M2 (156). As such, mirror M2 is saidto be located a distance f1 from lens L1, where f1 is representative ofthe focal length of lens L1. Between lens L1 and mirror M2, laser beam88 passes through lens L2, indicated at 154. Due to the orientation oflens L2 (L2 is a cylinder lens positioned such that its focusingdirection is generally perpendicular to the focusing direction of lensL1), lens L2 does not effect the shape of laser beam 88 in thecross-scan direction. Additionally, folding mirror M1 (155) acts todirect laser beam 88 at scanner mirror M2.

Scanner mirror M2 rotates to scan laser beam 88 in a raster patternacross the surface of film 66. Located halfway (proximate the midpoint)between scanner mirror M2 and the film 66 is flexible lens L3. Inparticular, flexible lens L3 is located at a distance which is twice thefocal length (2f3) of flexible lens L3, and the film 66 is located adistance from flexible lens L3 which is also twice the focal length(2f3) of flexible lens L3. As such, mirror M2 and the photosensitivefilm 66 are located at the conjugate points of flexible lens L3.

In FIG. 7, an enlarged optical diagram showing one exemplary embodimentof the relationship between scanner mirror M2, flexible lens L3 and thefilm 66 in the cross-scan direction is shown. The novel opticalconfiguration in accordance with the present invention, including thepositioning of flexible lens L3 between scanner mirror M2 and the film(or scanned) plane 66 may also operate as a mechanism or means forwobble correction. It is recognized that even with a small mirrorpointing error between two facets, the beam wobble at the film plane issignificant enough such that it may cause artifacts in the image exposedon the film 66. For example, assuming an optical pointing angle error of10 arcsec and a distance of 137 mm between the scanner mirror and thefilm, the wobble at the film is 6.6 micrometers.

As shown in FIG. 7, the beam wobble is depicted by directional arrow162. A number of items may contribute to beam wobble. For example, inaddition to beam wobble due to mirror pointing errors, the scanner motor138 shaft may wobble (possibly due to bearing tolerance), whichcontributes to the overall beam wobble at the film plane 66.

The novel optical configuration including flexible lens L3 is used as amechanism or means for wobble correction. The laser beam 88 is focusedto a line on the scanner mirror M2, narrower in the cross-scandirection, which is reimaged to the film 66 through flexible lens L3(indicated at 164). As previously described herein, the laser beam 88may wobble, indicated by directional arrow 162. As such, the opticalpath of laser beam 88 between mirror M2 and the film 66 is adjusted byflexible lens L3, indicated by dashed lines 166. Flexible lens L3operates to redirect the displaced laser beam 166 to the desiredlocation on film 172, indicated at 164. Due to the plano-convex flexiblelens L3, even if the laser beam 88 is shifted due to wobble effects,flexible lens L3 redirects the laser beam 88 to the desired location 164on film 66. As such, flexible lens L3 provides for correction for beamwobble.

In FIG. 8, an optical diagram illustrating operation of the novel lensconfiguration in the in-scan direction, in accordance with the presentinvention, is generally shown at 170. Collimated laser beam 88 (at 172)is emitted from laser assembly 76 and transmitted through lens L1 (at174) to lens L2 (at 176). In the in-scan direction, lens L1 does notaffect the shape of laser beam 88. Lens L2 operates to focus the laserbeam 88 in the in-scan direction onto the film 66. As such, the distancebetween lens L2 and the film 66 is equal to the focal length f2 of thelens L2.

Between lens L2 and the film 66, the laser beam 88 is redirected bymirror M1 (at 178) to the rotating scanner mirror M2 (at 180). Therotating scanner mirror M2 directs the laser beam 88 along a scan line184 across the film plane 66 as it rotates. In FIG. 8, the laser beam 88is shown in a first position 186, and a second rotated position 188,relative to the first position 186. As the rotating scanner mirror M2scans the laser beam 88 in the in-scan direction, the laser beam 88passes through flexible lens L3 (at 182). Flexible lens L3 does notaffect the shape of laser beam 88 in the in-scan direction.

In one exemplary embodiment, the laser beam 88 exiting the laserassembly 76 collimator 134 has an elliptical shape, with 1/e² diametersof approximately 1.1 mm and 4.0 mm in the cross-scan and in-scandirections, respectively. In the cross-scan direction, the laser beam 88is focused by L1, f1=95.6 mm onto the scanner mirror M2 surface. Theimage on the scanner mirror M2 surface is imaged through the flexiblelens L3, having a focal length f3 equal to 34.1 mm, onto the film 66. Inthe in-scan direction, cylindrical lens L2 having a focal length f2equals 192 mm, focuses the collimated laser beam 88 to the film plane 66directly. In one preferred embodiment, the nominal laser beam size atthe film 66 is 60 micrometers FWHM (full width at half maximum) in thecross-scan direction and 40 micrometers (FWHM) in the in-scan direction.

2. Lenses L1 and L2

In FIG. 9, the optical configuration of lens L1 and lens L2 are shown inperspective view generally at 200. In one preferred embodiment, lens L1and lens L2 are plano-convex cylinder lenses, and can be similar in sizeand shape, and in one embodiment generally rigid. As shown in FIG. 9,and described herein, the focusing direction of lens L1 and lens L2 areoriented generally perpendicular to each other. As such, lens L1 effectsthe shape of laser beam 88 in the cross-scan direction and lens L2effects the shape of laser beam 88 in the in-scan direction.

Lens L1 and lens L2 are tilted or angled from a position which isperpendicular relative to the optical axis (or optical path) as definedby laser beam 88. By tilting lens L1 and lens L2, the reflected portionof laser beam 88, indicated as reflected beam 146 and reflected beam147, can be controlled. In the exemplary embodiment shown, the reflectedbeam 146 is aimed and collected at absorbing surface 142 to avoid lightscattering. The control of reflected beam 147 allows lens L1 to act as abeam splitter. Alternatively, reflected beam 147 could also be directedto a light absorbing surface. The reflected beam from both surfaces ofL1 (the flat or planar surface and the convex surface), represented byreflected beam 147, is directed to the feedback sensor 140 whichprovides a feedback signal representative of the laser beam 88. The useof lens L1 as a beam splitter is described in detail later in thespecification.

Referring to FIG. 9a, a perspective view illustrating an exemplaryembodiment of lens L1 or lens L2 is shown for explanation of theorientation of lens L1 and L2, and the tilting of lens L1 or L2 relativeto the optical path defined by laser beam 88. In particular, lens L1includes a longitudinal axis 202a, a transverse axis 203a, and a normalaxis 204a. Similarly, lens L2 includes a longitudinal axis 202b, atransverse axis 203b, and a normal axis 204b. In operation, transverseaxis 203a and transverse axis 203b are perpendicular to the optical pathdefined by laser beam 88. While transverse axis 203a and transverse axis203b remain stationary, lens L1 and lens L2 are tilted or angledrelative to the optical path 88 by rotating lens L1 about transverseaxis 203a, and rotating lens L2 about transverse axis 203b. As such,longitudinal axis 203a is not perpendicular to the optical path 88, andlongitudinal axis 203b is not perpendicular to the optical path 88.

The tilt of lens L2 serves a dual purpose. In addition to allowingreflected light to be dumped (or directed) onto the absorbing surface142, it is possible to tune the focal length of the lens L2 by varyingthe angle of lens L2. L2 is rotatable about its transverse axis. Amechanism is provided for rotating lens L2 about its transverse axis. Inparticular, during the manufacturing and assembly of the optical scannerassembly 50, lens L2 can be rotated (or tilted), about an axis (itstransverse axis) that is parallel to the in-scan direction of the laserbeam 88, to change its focal length for tuning/calibrating the focallength of lens L2 to be positioned at film 66. In one exemplaryembodiment, a rotation angle adjustment of lens L2 from 10° to 40°yields a focal length change of approximately 15%.

In FIG. 10, a representative plot of one exemplary embodiment of thefocal length of lens L2 relative to the tilt angle is shown. In thisembodiment, lens L2 is a 150 mm lens. By adjusting the tilt angle oflens L2 (by rotating lens L2 about its transverse axis, wherein the tiltangle is defined as the angle between the longitudinal axis of lens L2and a position wherein the longitudinal axis of lens L2 would beperpendicular to the optical path), the focal length of lens L2 isadjusted or "tuned" for focusing on the film 66, in the in-scandirection. In a conventional optical system, the method of compensatingor adjusting for focal length variation of a lens similar to L2 would beto displace the lens along its optical axis. Such a method requires morephysical space in the optical scanner assembly to allow for tuningadjustment and displacement of the lens. The novel technique inaccordance with the present invention uses a simple plano-convexcylinder lens in which the focal point is adjusted or "tuned" throughchanging of the tilt angle of the lens. The transverse axis of lens L2remains stationary. The present technique is useful for reducing thecomplexity of the optical scanner assembly design and maintains acompact size for the optical scanner assembly. Additional space withinthe optical scanner assembly for adjustment and displacement of the lensalong the optical axis is no longer necessary.

Lens L1 and lens L2 have diffraction limited optical characteristics. Aswell known to those skilled in the art, since lens L1 and lens L2 havediffraction limited optical characteristics, they may be used to focus alaser beam on a scanned surface, wherein a predictable focus spot size(and position) is achieved across the scanned surface which can becalculated based on the physical characteristics of the lens. As usedherein, the term "diffraction limited" can be defined as the property ofan optical system, whereby only the effects of diffraction determine thequality of the image it produces. The term "diffraction limited lens"can be defined as a lens with aberrations corrected to the point thatresidual wave front errors are substantially less than 1/4 the wavelength of the energy being acted upon. See, the Photonics Dictionary,45st Edition, 1995 (Laurin Publishing, 1995).

Cylinder lens L1 and cylinder lens L2 can be similarly constructed. InFIG. 11, a cross-sectional view of a cylinder lens is generally shown at210. The cylinder lens 210 can be similar to cylinder lens L1 and/orcylinder lens L2. The cylinder lens 210 is a cylinder lens having aplano-convex optical shape. Preferably, the cylinder lens is generallyrigid. As such, the cylinder lens 210 includes a first, generally flat(or planar) surface 212 and a second, generally curved (or convex)surface 214. In one exemplary embodiment, the cylinder lens 210 includesa first substrate 216 and a second substrate 218, which are constructedof different materials. The first substrate 216 may beconstructed/formed of glass and the second substrate 218 may beconstructed/formed of a photopolymer. It is recognized thatalternatively, the cylinder lens 210 can be formed of a unitary, solidmolded material, such as glass. In one exemplary embodiment, thecylinder lens 210 (L2) first substrate 216 has a length of 25 mm and awidth of 25 mm, and the second substrate 218 has a length of 15 mm and awidth of 7.5 mm.

Cylinder lens 210 can be constructed/formed using a unique moldingprocess. In one exemplary embodiment, cylinder lens 210 may be formedusing the process steps shown in FIGS. 13, 14 and 15. In reference toFIG. 13, a mold 220 is provided having a top surface 222 which is curvedcorresponding to the desired curvature of the cylinder lens secondcurved surface 214 (for example, a concave surface will form a convexlens surface). In one exemplary embodiment, the mold 220,may be formedof glass, wherein the curved top surface 222 is ground or diamond cut tothe desired shape. The mold curved surface 222 is provided with anon-stick coating, indicated at 224. In one exemplary embodiment, asuitable non-stick coating is a Silane coating, commercially availablefrom PCR, Inc. in Gainesville, Fla. A computer controlled dispenser 226may be provided for dispensing a UV curable photopolymer 228 which formsthe cylinder lens second substrate 218. Dispenser 226 is operated todispense UV curable photopolymer in discrete droplet form onto the mold220 assembly including non-stick coating 224. In one exemplaryembodiment, the UV curable photopolymer is Summers Laboratory's J-91,located in Fort Washington, Pa. The dispenser 226 dispensesapproximately 7 droplets per inch, having a droplet weight ofapproximately 1.5 mg.

In reference to FIG. 14, the first substrate 216 is placed over thecharged mold 220, sandwiching the UV curable photopolymer 228 betweenthe first substrate 216 and the mold curved surface 222. In reference toFIG. 15, a UV light source 230 is provided for curing the cylinder lensassembly 210. The UV light source 230 is positioned over the lens andmold assembly for an amount of time required for curing the photopolymerfirst substrate 216 onto the second substrate 218. After curing, thecylinder lens 210 may be removed from the mold 220. Due to the non-stickcoating 224, the cylinder lens may be easily removed from the mold 220.

3. Laser Feedback Control System

The novel optical configuration of lens L1 effectively allows lens L1 tobe utilized as a "beam splitter" in a laser feedback control system. Aspreviously stated herein, the tilting of lens L1 allows the reflectedbeam 147 of laser beam 88 to be directed to photosensor 140, such thatit may be used in a feedback system for monitoring and stabilizing thelaser assembly 76 (see, FIG. 9 and FIG. 9a). Although the lens L1transverse axis remains perpendicular to the optical path defined bylaser beam 88, the longitudinal axis is rotated about the transverseaxis such that the longitudinal axis is not perpendicular to the opticalpath, thereby directing reflected beam 147 at photosensor 140. In FIG.16, a block diagram is generally shown at 240, showing lens L1 as a beamsplitter in a laser feedback control system. As shown in FIG. 16, andsimilar to operations previously described herein, laser assembly 76emits (produces) laser beam 88 which is transmitted through lens L1. Aportion of the laser beam 88 is reflected off the surface of lens L1,which has previously been described herein as reflected beam 147. Due tothe novel tilted configuration of lens L1, reflected beam 147 isdirected to the active region of photosensor 140. In one exemplaryembodiment, 90% of the laser beam is transmitted through lens C1 and 10%of the laser beam is reflected to photosensor 140 as reflected beam 147.

Photosensor 140 is responsive to the reflected beam 147 for providing anoutput signal 242 to laser driver 74 which is respresentative of thepower of the reflected beam 147. In response to feedback signal 242 andimage signal 84, laser driver 74 provides modulated output signal 86 tolaser assembly 76.

In FIG. 17, a top view of an exemplary embodiment of the use of the lensL1 in a laser feedback control system is shown at 244. As shown in FIG.17, cylinder lens L1 includes a top surface 246 and a bottom surface248. The reflected beam 147 is comprised of reflections off of thecylinder lens top surface 246 (convex surface), indicated at 254, andbottom surface 248 (flat or planar surface), indicated at 252.Correspondingly, the photosensor 140 includes an active region 250 whichis large enough to receive the reflected beams 252, 254 from the topsurface 246 and the bottom surface 248.

Laser assembly 76 emits a collimated light beam in the form of laserbeam 88 which is transmitted through lens L1. The reflected beam 247represents the reflected portion (feedback signal) which reflects off oflens L1 and is directed towards photosensor 140. In particular, firstreflected portion 252 is reflected from the cylinder lens bottom surface248, and second reflected portion 254 is reflected from the cylinderlens top surface 246, onto the photosensor 140 active region 250.

In FIG. 18, a side view of the lens feedback control system is shown at256. In the cross-scan direction, reflected beam 252 from bottom surface248 is reflected directly onto photosensor 140 (active region 250). Thereflected beam is convergent from the top surface. In thisconfiguration, the focal point is on reflected side. It is noted thatsince top surface 246 is convex shaped, the reflected beam 252 from topsurface 246 reaches a focal point 255 approximately midway before it isincident onto the photosensor 140.

4. Flexible Lens L3

In FIG. 19, flexible lens L3 is generally shown in perspective view. Inthe exemplary embodiment shown, flexible lens L3 is a cylinder lenshaving a plano-convex optical shape. The flexible lens L3 is formed of agenerally flexible material which allows flexible lens L3 to be easilyshaped to a desired curvature, such as is required by the opticalscanner assembly 60. The flexible lens L3 is flexible enough to bewrapped onto a guide. The flexible lens L3 is capable of being uniformlyflexed beyond a 180° arc, while maintaining and exhibiting diffractionlimited optical characteristics, and as such, allows the flexible lensL3 to be used in a laser imaging system suitable for medicalapplications.

In reference to FIG. 20, flexible lens L3 is a relatively thin,ribbon-like lens. Flexible lens L3 is a flexible, diffraction-limitedlens which lends itself most readily to the production of long (severalinches) positive cylinder lenses that can be easily bent into arbitraryshapes, such as the 180° arc shown. In particular, flexible lens L3 canbe utilized in one-dimensional laser scanning systems, in which a beamof light is scanned over a considerable distance (many inches), such asthe laser imaging system shown in FIG. 1. Referring to FIG. 21, flexiblelens L3 can be flexed beyond a 180° arc, allowing the flexible lens L3to be used in many applications which require the use of a flexiblelens, either for obtaining desired optical characteristics or due tospace constraints, without causing damage to the lens or damaging theoptical characteristics of the lens. Flexible lens L3 is capable ofbeing "flexed" or "bent" in over a 180° arc, while exhibiting andmaintaining diffraction limited optical characteristics. As well knownto those skilled in the art, by maintaining diffraction limited opticalcharacteristics if a flexible lens in accordance with the presentinvention is used to focus a laser beam on a scanned surface, apredictable focus spot size (and position) is achieved across thescanned surface which can be calculated based on the physicalcharacteristics of the lens. As used herein, the term "diffractionlimited" can be defined as the property of an optical system, wherebyonly the effects of diffraction determine the quality of the image itproduces. The term "diffraction limited lens" can be defined as a lenswith aberrations corrected to the point that residual wavefront errorsare substantially less than 1/4 the wavelength of the energy being actedupon. See, the Photonics Dictionary, 41st Edition, 1995 (LaurinPublishing, 1995).

Known conventional polygonal scanning systems often require the use of arigid torodial or rigid cylinder shaped lens as part of field-flatteninglenses for producing an image on photosensitive film. Such lenses arecomplex, costly and difficult to produce. These lens have typically beenground out of glass, which do not lend themselves to being easily bentinto arbitrary shapes. The novel flexible lens L3 in accordance with thepresent invention lends itself most readily to the production of long,positive cylinder lenses that can be easily bent into arbitrary shapes.Further, the method of construction described herein allows theconstruction of such lenses using a simple unique cast and cure systemfollowed by using a simple guide for bending the flexible lens into therequired shape for a desired application. It is recognized that analternative method to construction of flexible lens L3 would be toinjection-mold the lens out of plastic. However, it is also recognizedthat creating long, diffraction-limited cylinder lenses of the typediscussed herein would be quite difficult using injection moldingprocesses.

In FIG. 22, a cross-sectional view of a flexible cylinder lens isgenerally shown at 260. The flexible cylinder lens 260 can be similar toflexible lens L3 for use in an optical scanner assembly. In referencealso to FIG. 23, a longitudinal cross-sectional view of the flexiblecylinder lens 260 is shown. In one exemplary embodiment, the flexiblecylinder lens 260 is a multi-layered lens. The flexible cylinder lens260 includes a first, optical substrate 262, a second, structural orsupport substrate 264, and a third, optical substrate 266. In theexemplary embodiment shown, first substrate 262 is formed of aphotopolymer. Second substrate 264 is preferably a thin, flexiblepolymeric or plastic substrate. In one embodiment, it is recognized thatthe second substrate 264 may be formed of a polyester or polycarbonate.Additionally, the third substrate 266 may also be formed of aphotopolymer.

In one exemplary embodiment, the flexible cylinder lens 260 is 233millimeters long having a 33.4 mm focal length with a 3 mm highaperture. The photopolymer used for the first substrate 262 and thethird substrate 266 is commercially available from Summers Laboratoriesunder the tradename J-91. The second substrate 264 is formed of a 0.006inch thick layer of polycarbonate, having a 15 mm by 251 mm substratesize.

In FIGS. 24-27, one preferred embodiment of forming flexible cylinderlens 260 is shown. In FIG. 24, a cylinder mold 270 is provided having acurved top surface 272 which corresponds to the desired shape of thirdsubstrate 266. In one preferred embodiment, the mold is made of glass,wherein the curved top surface 272 is ground to the desired shape.Alternatively, a non-glass mold can also be diamond turned to thedesired shape. The cylinder mold 270 includes a non-stick coating 274coated over the curved top surface 272. The non-stick coating 274 doesnot allow photopolymer to stick to the mold top surface 272. In onepreferred embodiment, the non-stick coating 274 is a silane coating,commercially available from PCR, Inc.

A dispenser 276 is provided for dispensing photopolymer onto the moldtop surface 272. Preferably, the dispenser 276 is a computer-controlleddispenser capable of dispensing a photopolymer material in the form ofdiscrete droplets.

The cylinder mold 270 is charged operating the dispenser 276 to dispensediscrete droplets of photopolymer, indicated at 278, onto the topsurface 272. The discrete droplets 278 are sized and spaced to collecttogether into a layer, without voids or excess when the next substrateis positioned onto the mold 270. In one exemplary embodiment, thedroplet are dispensed at a rate of 1 droplets per 2 mm, having a dropletweight of 0.6 mg.

Referring to FIG. 25, the second substrate 264, formed of a flexibleplastic, is positioned over the droplets 278 and laid onto the chargedcylinder mold 270. In FIG. 26, a UV light source 280 is provided. Lightsource 280 is positioned over the resulting assembly 282 for a period oftime required for curing the photopolymer 278 and mold assembly 282. Atthis stage, complete curing of the mold assembly is not necessary. It isrecognized that the purpose of curing in this step is to avoid the lensbeing pulled away from the mold 270, which may occur if the entireflexible cylinder lens 260 were cast and cured at once.

Referring to FIG. 27, the UV light source 280 is removed and the mold270 is again charged. Dispenser 276 is controlled for dispensingdiscrete photopolymer droplets 283 onto the charged substrate 264 toform substrate 262.

Referring to FIG. 28, a top mold substrate 284 is placed onto the moldedconstruction over the dispensed droplets 283. In reference to FIG. 29,the entire mold assembly is placed under UV light source 280 for aperiod of time required for complete curing of the mold assembly.

In reference to FIG. 30, the top mold substrate 284 is thin enough toallow it to flex, and has also been treated with a non-stick coating,such as a Silane coating. As such, the top mold substrate 284 may beeasily "popped" off the cured molded construction for removal offinished flexible cylinder lens 260. In reference to FIG. 29, it 4A isrecognized that external means 286 may be used for aiding in removal ofthe flexible cylinder lens 260 from the molded assembly, such asapplying pressure to the molded assembly.

5. Attenuator System

In FIG. 32, an exemplary embodiment of the laser beam shaping anddirecting system 100 in accordance with the present invention is shown,which may further include an attenuator 290. In one embodiment, theattenuator 290 is positioned between lens L1 and lens L2. Attenuator 290is a variable density attenuator formed of a single unitaryconstruction. The attenuator 290 may function to further shape laserbeam 88, and in particular, for controlling and calibrating the power oflaser beam 88 transmitted to the scanner mirror M2. Attenuator 290 ispositioned between the laser mechanism and L2, and in the embodimentshown, adjacent L2. The unibody attenuation mechanism has a densitygradient which is oriented perpendicular to the longitudinal axis of L2.The unique combination of the variable density attenuator 290 and L2results in no change in the focusing of the laser beam at the focus spoton the photosensitive film.

Known attenuators used in conventional optical scanning systems utilizecross-polarizing attenuators. Such attenuators include two polarizedfilters which are crossed for attenuating a laser beam passing throughthe crossed filter portion.

In FIG. 33, a top view of one exemplary embodiment of the novelattenuator in accordance with the present invention is shown at 290.Attenuator 290 is a variable density attenuator, wherein the amount oflaser beam attenuation varies (or increases) from first side 292 tosecond side 294, indicated by attenuation arrow 296. In FIG. 34, alongitudinal cross section of attenuator 290 taken along line 34--34 ofFIG. 33 is shown. The attenuator 290 includes an attenuator substrate298 having a varying reflective coating 300. In one exemplaryembodiment, the attenuator substrate 298 is formed of glass, and theattenuator coating 300 is a metallic coating, the thickness of whichincreases between first side 292 and second side 294.

The attenuator 290 is a unibody attenuator, and as such, does notrequire two separate crossed polarizers or lenses to attenuate a laserbeam passing therethrough. Further, the variable density unibodyattenuator 290 is a linear density wedge. As such, the optical densityof the attenuator mechanism 290 increases proportionally with thedistance across the attenuator 290.

In operation, the attenuator top surface 302 is reflective (such as amirror), not absorbing. As such, the farther one moves from first side292 closer to second side 294, the more reflective (and lesstransmissive) attenuator 290 becomes. In FIG. 35, a graph showing theplot of the optical density of one embodiment of attenuator 290 versusthe distance or position longitudinally along attenuator 290 (indicatedby density gradient directional arrow 296) is shown. As shown, theoptical density representative of the amount of attenuation increasesproportionally the farther one moves along the attenuator 290 indirection 296 (termed "density gradient").

In FIG. 36, the effect of attenuator 290 on the position of laser beam88 is shown (in the in-scan direction). The attenuator 290 densitygradient is indicated by directional arrow 296. The attenuator densitygradient is oriented perpendicular to the longitudinal axis of thesecond cylinder lens. As indicated at 310, the gaussian intensityprofile of laser beam 88 is merely shifted by attenuator 290 as laserbeam 88 passes through attenuator 290. It is recognized that since lensL2 is a plano-convex cylinder lens, the shifting of laser beam 88 byattenuator 290 does not effect the focusing of laser beam 88 onto thefilm 66. This unique optical configuration provides for the combinationof a variable density attenuator 290 and L2 which results in no changein the focus spot at the photosensitive film positioned on the internalsurface of the drum.

In FIG. 37, a graphical representation of the laser beam 88 intensityand position on side 306 before passing through attenuator 290 is shown.As shown in FIG. 37, the laser beam 88 is centered about axis 312. InFIG. 38, laser beam 88 is shown at location 308 after passing throughthe attenuator 290. As such, it is noted that the shape of laser beam 88has not changed, it has only shifted relative to central axis 312. Inone exemplary embodiment of the optical scanner assembly in accordancewith the present invention, the attenuator 290 shifts the laser beam 88100 microns.

In FIG. 39, one exemplary embodiment for calibration of laser beam 88using attenuator 290 is shown. As shown in FIG. 39, the attenuator 290is positioned for calibration of laser beam 88 during the manufacturingprocess of the optical scanner assembly 50. Calibration of the positionof attenuator 290 is accomplished utilizing a motor 316 coupled to acontroller 72. The motor 316 is electrically coupled to controller 72(indicated at 319), and mechanically coupled to attenuator 290,indicated by mechanical connection 320. Motor 316 is responsive tocontroller 72 for moving attenuator 290 a desired distance. In oneexemplary embodiment, the motor 316 is a screw motor which ismechanically coupled to the optical scanner assembly 50.

In FIG. 40, a perspective view illustrating one exemplary embodiment ofan optical scanner assembly in accordance with the present invention isgenerally shown. The optical scanner assembly 330 can be similar to theoptical scanner assembly 50 described previously herein, and includeslaser beam shaping and directing system 100. In particular, the opticalscanner assembly 330 includes laser beam shaping and directing system100 contained within an optical scanner housing 332. The optical scannerhousing may be positioned within the film exposure assembly 34 as partof a laser imaging process, and is mechanically coupled to the opticstranslation system 52.

The optical scanner housing 332 includes a flexible lens holder 334having a guide 336, an optics module base 338 and a laser driver boardenclosure 340. The scanner motor 138 is positioned within the opticalmodule base 338. Flexible lens L3 is located within flexible lens holder334. In particular, flexible lens L3 is inserted within lens guide 336,which imparts a desired curvature (such as the 180° arc shown) to theflexible lens L3. The laser driver 74 is located within the laser driverboard enclosure 340. Additionally, a scanner speed sensor 342 andstart-of-scan detector 346 are coupled to the optical scanner housing332.

In FIG. 41, another perspective view of the optical scanner 330 isshown. As shown in FIG. 41, the optical scanner housing 332 includeslens L2 holder 350, attenuator filter holder 352, and lens L1 holder354. Accordingly, lens L2 is attached to optics module base 338 usinglens L2 holder 350, attenuator 290 is attached to the optics module base338 using attenuator filter holder 352, and lens L1 is attached to theoptics module base 338 using lens L1 holder 354. Motor 316, as shown, isa linear actuator (e.g., screw motor) for adjusting the position ofattenuator 352. The holders 350, 352 and 354 maintain lens L1,attenuator 290, and lens L2 in optical alignment along the optical pathdefined by laser beam 88 shown.

The optical scanner assembly in accordance with the present inventionmay be used in a laser imaging system which is suitable for use inmedical imaging applications. Operation of such a system will bedescribed in the following paragraphs. In reference to FIG. 1, theimaging system 30 can be a medical imaging system. Photosensitive filmis stored within the film supply mechanism 32. The film transport system40 allows the photosensitive film to be moved between the film exposureassembly 34, the film processing station 36, and the film receiving area38. The film supply mechanism 32 feeds a piece of film along the filmtransport path 44 into the film exposure assembly 34 for exposing adesired image on the photosensitive film using the optical scannerassembly in accordance with the present invention. After exposure of thedesired image on the photosensitive film, the photosensitive film ismoved along the film transport path 44 to the film processing station36. The film processing station 36 develops the image (through theapplication of heat) on the photosensitive film. After film development,the photosensitive film is cooled and transported to the film receivingarea 38, where it may be picked up by the laser imager operator.

Referring to FIG. 42, a block diagram illustrating one exemplaryembodiment of operation of an optical scanner assembly in accordancewith the present invention, located within a film exposure module, isshown. Referring also to FIGS. 2 and 3, once a piece of photographicfilm 66 is positioned on the film platen 62, a desired image may beexposed on the film 66 using optical scanner assembly 50.

Digital image data 350 is input to controller 72, indicated at 352. Thedigital image data may be generated by magnetic resonance (MR), computedtomography (CT), or other types of scanners, as previously describedherein. The digital image data is a sequence of digital image valuesrepresentative of the image to be scanned. Upon receipt of the digitalimage data 350, controller 72 processes the digital image data togenerate a sequence of digital laser drive values (i.e., exposurevalues), which are input to the laser driver 74, indicated as imagesignals 84. The digital laser drive values (image signals) 84 arerepresentative of the image to be exposed on the photosensitive film 66,and as such, have been previously described herein as image signals 84.

Based on image signal 84 and a feedback signal 242 from photosensor 140,laser driver 74 provides a corresponding laser driver modulated outputdriver signal 86 to laser assembly 76 for producing laser beam 88representative of the image to be exposed on the photographic film 66.Laser beam 88 passes through the optical scanner assembly laser beamshaping and directing system as previously described herein, whichincludes passing through first optical mechanism 78, attenuator 290,second optical mechanism 80, and scanning and directing system 82 forexposure of the desired image on the photosensitive film 66.

As previously described herein, first optical mechanism 78 (includinglens L1 and flexible lens L3), and second optical mechanism 80(including lens L2) function to shape the laser beam in two separatedirections, which are perpendicular to each other. The first opticalmechanism 78 functions to shape the laser beam 88 profile in a firstdirection (but not a second direction) for focusing the laser beam 88 ina first direction on the film 66, as previously described herein.Similarly, the second optical mechanism 80 functions to shape the laserbeam 88 in the second direction (but not the first direction) forfocusing the laser beam 88 in the second direction on the photosensitivefilm 66. Further, first optical mechanism 78 provides a feedback signal147 to photo sensor 140. Photo sensor 140 provides a feedback signal 242to laser driver 74, representative of the laser beam 88. Based onfeedback signal 242 and image signal 84, laser driver 74 providesmodulated signal 86 to laser assembly 76. Attenuator 290 functions tofurther shape laser beam 88, as described herein, for controlling andcalibrating the power of laser beam 88 transmitted to the scanning anddirecting system 82.

Scanning and directing system 82 includes a scanner and mirror systemfor directing the laser beam 88 to the desired location on film 66 andscanning the laser beam 88 across the film 66 in a raster pattern forexposing the desired image on film 66. Controller 72 provides controlsignals 358 to scanning and directing system 82, and receives controlsignal 360, e.g., a start-of-scan signal, from detector 346 or speedsignal from scanner speed sensor 342, from scanning and directing system82. Similarly, optics translation system 52 receives control signals 362from controller 72, and provides corresponding control signals 364 tocontroller 72. As previously described herein, within scanning anddirecting system 82, laser beam 88 is reflected by the folding mirror M1such that it is incident on the scanner mirror M2. In one preferredembodiment, the scanner mirror M2 is a two-sided mirror which is mountedon the shaft through an adapter 137 of the scanner motor 138.

Upon operation of scanner motor 138, indicated by control signal 358,the scanner mirror M2 is rotated and the laser beam 88 is reflectedoutward radially, and transmitted through flexible lens L3 for exposingthe film 66 in an image-wise raster pattern. Both sides of scannermirror M2 are used for directing a laser beam 88 through flexible lensL3 to expose the film 66.

In one preferred embodiment, scanning and directing system 82 is adouble scanning system. In particular, an image line is scanned twicewith the same data on the photosensitive film 66. Double scanning hasbeen found to improve image sharpness over single scanning, and makesscan line invisible under normal viewing conditions. The two scannedlines in an image line are scanned by the two sides of mirror M2 duringone scanner rotation. This technique reduces banding due to scannermirror pointing error. As the scanning and directing system 82 scans animage in a raster pattern on the photosensitive film 66, the opticstranslation system 52 moves the optical scanner assembly 50 along thelongitudinal axis 56 of the drum 54, such that the entire image may beexposed on the film 66. In one preferred embodiment, the opticstranslation system cooperates with the optical scanner assembly 50through controller 72 such that an image may be actively exposed on thefilm 66. As such, the optics translation system does not stop theoptical scanner assembly 50 at the location of each scan line, and theoptics translation system 52 is in a rest position during scanning of ascan line on the film 66 by the optical scanner assembly 50 (termed"continuous scanning operation" as known by those skilled in the art).The optics translation system 52 slowly moves the optical scannerassembly 50 in a uniform manner during scanning of the image scannedlines on the photosensitive film 66. In this embodiment, the image scanlines do not run perpendicular to the longitudinal axis of the drum 56,but rather results in an image formed by scan lines which areapproximately perpendicular to the longitudinal axis 56 of the drum 54.

Upon completion of exposure of the desire image or images on film 66 bythe optical scanner assembly 50, optical scanner assembly 50 is moved toa start position by optics translation system 52, ready for exposure ofanother image on another piece of film. The exposed photosensitive film66 is transported from the exposure module 34 using film transportsystem 40 to the film processing station 36 for thermal processing ofthe photosensitive film as previously described herein.

Having described the exemplary embodiments of the invention, additionaladvantages and modifications will readily occur to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. For example, the scanning assembly inaccordance with the present invention may be used in other laserscanning application, such as film digitization. Therefore, thespecification and examples should be considered exemplary only, with thetrue scope and spirit of the invention being indicated by the followingclaims.

What is claimed is:
 1. An optical scanner assembly for exposing an imageon a scanned surface, the optical scanner assembly comprising:a lasermechanism for producing a modulated laser beam representative of theimage to be exposed on the scanned surface, the laser beam defining anoptical path between the laser mechanism and the scanned surface; alaser beam shaping system positioned along said optical path forfocusing and shaping the laser beam onto the scanned surface; a scanningand directing system positioned along said optical path for directingthe laser beam to the scanned surface and scanning the laser beam acrossthe scanned surface in an image-wise pattern; a single unibody variabledensity attenuation mechanism positioned along said optical path forpower attenuation of the laser beam along a single polarization axiswhich is shifted laterally of said optical path, wherein the unibodyattenuation mechanism is a linear density wedge; and an optical devicefor correcting said lateral shift of said laser beam.
 2. The opticalscanner assembly of claim 1, wherein the laser beam shaping systemincludes:a first cylinder lens positioned along the optical path forshaping and focusing the laser beam in a first direction; and a secondcylinder lens having a longitudinal axis extending therethrough,positioned along the optical path for shaping and focusing the laserbeam in a second direction;wherein the unibody attenuation mechanism hasa density gradient which is oriented perpendicular to the longitudinalaxis of the second cylinder lens.
 3. The optical scanner assembly ofclaim 2, wherein the unibody attenuation mechanism is located betweenthe laser mechanism and the second cylinder lens.
 4. The optical scannerassembly of claim 2, wherein the second cylinder lens has a focusingspot at the scanned surface, and wherein the combination of the unibodyattenuation mechanism and the second cylinder lens operate to maintainthe size, shape and position of the focusing spot at the scannedsurface.
 5. The optical scanner assembly of claim 1, further wherein theunibody attenuation mechanism is movable along an axis perpendicular tosaid optical path.
 6. The optical scanner assembly of claim 1, furthercomprising an adjustment mechanism coupled to the unibody attenuationmechanism for adjusting an amount of power attenuation of the laserbeam.
 7. The optical scanner assembly of claim 6, wherein the adjustmentmechanism for adjusting the unibody attenuation mechanism adjusts aposition of the unibody attenuation mechanism in a directionperpendicular to the optical path.
 8. The optical scanner assembly ofclaim 6, wherein the adjustment mechanism for adjusting the unibodyattenuation mechanism includes a linear actuator.
 9. The optical scannerassembly of claim 1, wherein the unibody attenuation mechanism has afirst end and a second end, wherein a degree of attenuation variesbetween the first end and the second end.
 10. The optical scannerassembly of claim 9, wherein the unibody attenuation mechanism ispositioned substantially perpendicular to the optical path having thelaser beam passing therethrough, and wherein the attenuation of thelaser beam power increases as the attenuation mechanism is moved from aposition proximate the first end to a position proximate the second end.11. The optical scanner assembly of claim 1, wherein the unibodyattenuation mechanism includes a first side and a second side, andwherein the unibody attenuation mechanism shifts a position of the laserbeam as it passes through the unibody attenuation mechanism from thefirst side to the second side.
 12. The optical scanner assembly of claim1, wherein the unibody attenuation mechanism further comprises:anattenuator support substrate having a major surface; and a varyingreflective material covering the major surface.
 13. The optical scannerassembly of claim 12, wherein the support substrate is constructed ofglass.
 14. The optical scanner assembly of claim 12, wherein the varyingreflective material is a metallic material.
 15. The optical scannerassembly of claim 12, wherein the attenuator support substrate includesa first end and a second end, and wherein a reflectivity density of thevarying reflective material increases from the first end to the secondend.
 16. The optical scanner assembly of claim 12, wherein the unibodyattenuation mechanism is partially transmissive, and wherein theattenuator support substrate includes a first end and a second end, andwherein the transmissive properties of the varying reflective materialdecrease from the first end to the second end.
 17. An optical scannerassembly used in an internal drum type scanner, for exposing an image ona photosensitive film, the optical scanner assembly comprising:a lasermechanism for producing a modulated laser beam representative of theimage to be exposed on the photosensitive film, the laser beam definingan optical path between the laser mechanism and the photosensitive film;a laser beam shaping system positioned along said optical path forfocusing and shaping the laser beam; a scanning and directing systempositioned along said optical path for directing the laser beam andscanning the laser beam radially across the photosensitive film in animage-wise pattern; a single variable density unibody attenuationmechanism having a first end and a second end, wherein a degree ofdensity varies from the first end to the second end, and wherein theunibody attenuation mechanism is positioned along the optical path forpower attenuation of the laser beam along a single polarization axis andfor laterally shifting said laser beam relating to said optical path;and an optical device for correcting said lateral shift of said laserbeam.
 18. The optical scanner assembly of claim 17, further wherein theunibody attenuation mechanism is adjustable.
 19. The optical scannerassembly claim 17, wherein an optical density of the unibody attenuationmechanism increases proportionally to a distance across the unibodyattenuation mechanism between the first end and the second end.
 20. Theoptical scanner assembly of claim 19, wherein the unibody attenuationmechanism is positioned substantially perpendicular to the optical pathhaving the laser beam passing therethrough, and wherein the attenuationof the laser beam increases as the laser beam is moved from a positionproximate the first end to a position proximate the second end.
 21. Theoptical scanner assembly of claim 17, wherein the unibody attenuationmechanism includes a first side and a second side, and wherein theunibody attenuation mechanism shifts a position of the laser beam as itpasses through the unibody mechanism from the first side to the secondside.
 22. The optical scanner assembly of claim 17, wherein the unibodyattenuation mechanism further comprises:an attenuator support substratehaving a major surface; and a varying reflective material covering themajor surface.
 23. The optical scanner assembly of claim 22, wherein thesupport substrate is constructed of glass.
 24. The optical scannerassembly of claim 22, wherein the varying reflective material is ametallic material.
 25. The optical scanner assembly of claim 22, whereinthe unibody attenuation mechanism is partially transmissive, and whereinthe attenuator support substrate includes a first end and a second end,and wherein the transmissive properties of the varying reflectivematerial decrease from the first end to the second end.
 26. A laserimaging system comprising:a film feed mechanism; a film exposuremechanism; a film processor mechanism; a film receiving area; and a filmtransport system for moving a piece of photosensitive film between thefilm feed mechanism, the film exposure mechanism, the film processormechanism, and the film receiving area;wherein the film exposuremechanism includes an optical scanner assembly having a single unibodyattenuation mechanism for power attenuation of a laser beam passingtherethrough, wherein the single unibody attenuation mechanism is alinear density wedge.
 27. The laser imaging system of claim 26, whereinthe optical scanner assembly is an internal drum type scanner.